Lemma 2.5 [1]}
Let \(A\)  be a spectral set in \(\mathbb {Z}_{N}\) , that does not generate \(\mathbb {Z}_{N}\) . Assume that for every proper subgroup \(H\)  of \(\mathbb {Z}_{N}\)  we have \(S-T(H)\) . Then \(A\)  tiles \(\mathbb {Z}_{N}\) .

